Fancy name for a dial turning from black to brownish
This is due to humidly getting into a watch case by way of faulty gaskets over the years attacking the dial and hands and caliber.. while damage occurs on the mechanical parts, the dial paint changes chiefly form an all black dial to brown or caramel color as one can see on the GMT in my scan.
This freak of nature is now highly prized to vintage collectors.
Arthur
One more example..The left has a black dial and the right a color change dial..